The invention relates to a method and a device for determining and selecting frequencies in at least two superimposing cellular communication systems using the same frequencies. The invention particularly relates to a method and device for allocating frequencies to a cellular communication system by simultaneously avoiding interferences between two superimposing communication systems using the same frequencies.
The prior art discloses two superimposing communication systems, a so-called indoor cellular system and an external cellular system outside a building, whereby the same frequencies are used by both systems. Such an indoor cellular system is also called a parasitic system because it benefits from the external cellular system by using free frequencies of the external system. Said parasitic systems are expected to operate with low field strengths for avoiding or reducing interferences with the superimposed system. According to the prior art a so-called macrocell calculates which channels, i.e. frequencies, are available for further use in the indoor system. It is thereby an essential aspect to determine how and, for example, up to which floor such parasitic system operates. Moreover, the prior art consequently shows that two superimposing cellular systems using the same frequencies can exist and function together, if the communication system has a sufficiently large capacity ("A Simulation Study of Urban In-Building Cellular Frequency Reuse", T. S. Rappaport, R. A. Brickhouse; IEEE Personal Communications, February 1997, page 19 to page 23).